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Influence of cement type and ceramic primer on retention of polymer-infiltrated ceramic crowns to a one-piece zirconia implant
RESEARCH AND EDUCATION
Influence of cement type and ceramic primer on retention of polymer-infiltrated ceramic crowns to a one-piece zirconia implant Nadja Rohr, Dr med dent,a Stefan Brunner, Dr med dent,b Sabrina Märtin,c and Jens Fischer, Prof Dr med dent, Dr rer natd
ABSTRACT Statement of problem. The best procedure for cementing a restoration to zirconia implants has not yet been established. Purpose. The purpose of this in vitro study was to measure the retention of polymer-infiltrated ceramic crowns to zirconia 1-piece implants using a wide range of cements. The effect of ceramic primer treatment on the retention force was also recorded. The retention results were correlated with the shear bond strength of the cement to zirconia and the indirect tensile strength of the cements to better understand the retention mechanism. Material and methods. The retention test was performed using 100 polymer-infiltrated ceramic crowns (Vita Enamic) and zirconia implants (ceramic.implant CI) The crowns were cemented with either temporary cement (Harvard Implant semipermanent, Temp Bond), glass-ionomer cement (Ketac Cem), self-adhesive cement (Perma Cem 2.0, RelyX Unicem Automix 2, Panavia SA), or adhesive cement (Multilink Implant, Multilink Automix, Vita Adiva F-Cem, RelyX Ultimate, Panavia F 2.0, Panavia V5 or Panavia 21) (n=5). Additionally ceramic primer was applied on the intaglio crown surface and implant abutment before cementation for all adhesive cements (Multilink Implant, Multilink Automix: Monobond plus; RelyX Ultimate Scotchbond Universal; Vita Adiva F-Cem: Vita Adiva Zr-Prime; Panavia F2.0, Panavia V5: Clearfil Ceramic Primer) and 1 self-adhesive cement containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP) (Panavia SA: Clearfil Ceramic Primer). Crown debond fracture patterns were recorded. Shear bond strength was determined for the respective cement groups to polished zirconia (n=6). The diametral tensile strength of the cements was measured (n=10). Statistical analysis was performed using 1-way or 2-way analysis of variance followed by the Fisher LSD test (a=.05) within each test parameter. Results. Adhesive and self-adhesive resin cements had shear bond strength values of 0.0 to 5.3 MPa and revealed similar retention forces. Cements containing MDP demonstrated shear bond strength values above 5.3 MPa and displayed increased retention. The highest retention values were recorded for Panavia F 2.0 (318 ±28 N) and Panavia 21 (605 ±82 N). All other adhesive and self-adhesive resin cements attained retention values between 222 ±16 N (Multilink Automix) and 270 ±26 N (Panavia SA), which were significantly higher (P<.05) than glassionomer (Ketac Cem: 196 ±34 N) or temporary cement (Harvard Implant semipermanent: 43 ±6 N, Temp Bond: 127 ±13 N). Application of manufacturer-specific ceramic primer increased crown retention significantly only for Panavia SA. Conclusions. Products containing MDP provided a high chemical bond to zirconia. Self-adhesive and adhesive resin cements with low chemical bonding capabilities to zirconia provided retention force values within a small range (220 to 290 N). (J Prosthet Dent 2017;-:---)
Implants made from zirconia are a promising alternative to the well-established titanium implants.1-4 However, when restored with zirconia crowns, chipping of the veneering ceramic has been recorded.5,6 An optimal
material for creating a restoration on zirconia implants has not yet been established. Materials with a low elastic modulus, such as polymer-infiltrated ceramic,7 might be able to buffer intraoral forces on the zirconia implant.
a
Postdoctoral student, Division of Dental Materials and Engineering, Department of Reconstructive Dentistry and Temporomandibular Disorders, University Center for Dental Medicine Basel, University of Basel, Basel, Switzerland. Private practice, Langenthal, Switzerland. c Laboratory Manager, Vita Zahnfabrik, Bad Säckingen, Germany. d Professor, Division of Dental Materials and Engineering, Department of Reconstructive Dentistry and Temporomandibular Disorders, University Center for Dental Medicine Basel, University of Basel, Basel, Switzerland. b
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Clinical Implications Self-adhesive and adhesive composite resin cements with only slight bonding capabilities to zirconia still achieve high crown retention. The use of a primer on the implant abutment affected the retention force of the crown only for Panavia SA.
Polymer-infiltrated ceramic shows slightly higher fracture load values than does feldspathic ceramic when used on zirconia.8 Zirconia implants are currently offered as 1-piece devices. Therefore, a restoration has to be cemented directly on the implant. The choice of the cement connecting crown and implant greatly relies on the restorative material used. For silica and polymer-infiltrated ceramics, cements with a high compressive strength such as adhesive resin cements are recommended to increase the fracture load of the system.8-12 Fracture load values of oxide ceramics are not influenced by cement type.12 However, cementation of oxide ceramic restorations with resin-based materials can improve their marginal adaptation.10 The application of 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing bonding agents can increase bond strength to zirconia13-18 because of an interaction between the hydroxyl groups of MDP and the cationic surface of zirconia.19,20 Establishing a microretentive structure on zirconia is difficult because zirconia, with its high crystalline content without any silica phase, is resistant to hydrofluoric acid etching.21 The effect of silanization on establishing a chemical bond between the hydrophilic zirconia surface and the hydrophobic resin cement remains controversial.13,21-25 Bond strength is measured using various methods each using macro- or microspecimens: shear tests, tensile tests, or push-out tests.26-28 The bond strength of resin cements to zirconia varies significantly according to the test design.26,28 The variability in results among these testing methods makes it difficult to establish a correlation between laboratory data and the clinical performance of tested materials.29-32 A more clinically related method of testing the retention capability of dental cement is the crown retention test design, where crowns are cemented under a defined load and pulled off in an axial direction after the cement has set.33-36 Thus, the purpose of this study was to evaluate the retention of polymer-infiltrated ceramic crowns on zirconia implants using a wide range of commercially available cement types. The interaction between the tensile retention and the shear bond strength of cements to zirconia, as well as their diametral tensile strengths, were evaluated. The effect of manufacturer-specific
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ceramic primer surface treatments on retention forces and shear bond strengths were additionally tested. The 5 hypotheses were that retention forces are higher for adhesive and self-adhesive cement than for temporary cements; that the application of primer on the crown and implant abutment increases retention forces; that shear bond strength of adhesive and self-adhesive cements to zirconia is higher than for temporary cements; that the application of primer on the zirconia surface increases the shear bond strength; and that diametral tensile strength of the cements differs significantly. MATERIAL AND METHODS For the retention test, 100 zirconia implants (ceramic.implant CI, vitaclinical; Vita Zahnfabrik) 4.5 mm in diameter were used. The roughness of the abutment surface was Ra=0.42 ±0.06 mm (n=3) (T1000/TKK50, Hommelwerke). The endosseous portions of the implants were embedded in epoxy resin (Araldite, RenCast CW20/Ren HY49; Bodo Müller Chemie) according to ISO 14801:2016 Dentistry-Implants-Dynamic loading test for endosseous dental implants. All implants had an endosseous length of 10 mm and were inserted with a 3 mm clearance between the implant neck and resin surface. One implant was scanned with an optical scanner (inEos Blue; Dentsply Sirona). A mandibular right first molar crown was designed (inLab SW4.0; Dentsply Sirona). One hundred polymer-infiltrated ceramic crowns (Vita Enamic; Vita Zahnfabrik) were milled (inLab MCXL; Dentsply Sirona). All crowns and implants were cleaned in a 96% ethanol ultrasonic bath for 4 minutes (TPC-15; Telsonic). The intaglio surface of each crown was etched with hydrofluoric acid (Ceramics Etch; Vita Zahnfabrik) for 60 seconds. Sixty-five crowns were cemented on the implants using 13 different cements according to the manufacturers’ recommendations (Table 1) (n=5). The cements were selected to cover a wide range of cement classifications, compositions, and manufacturers. Additionally, 35 crowns were cemented on implants with adhesive cements MLI, MLA, VAF, PF2, and PV5 and 1 self-adhesive cement with MDP (PSA) using ceramic primer on the intaglio surface of the crown and implant abutment (MLI, MLA: Monobond plus, Ivoclar Vivadent; RUL: Scotchbond Universal, 3MEspe; VAF: Vita Adiva Zr-Prime, Vita; PSA, PF2, PV5: Clearfil Ceramic Primer, Kuraray) (n=5). The crowns were filled with cement, placed on the implants, and loaded with 25 N for 10 minutes at room temperature. They were not light polymerized; all materials were allowed to autopolymerize. Excess cement was eliminated using foam pellets. After the cementation process, the specimens were stored in distilled water at 37 C for 24 hours. The crown retention testing was performed using a universal testing machine (Z020;
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Table 1. Cement materials and ceramic primer used Type
Cement
Code
Manufacturer
Lot No/Exp Date
Composition
Glass-ionomer cement
Ketac Cem
KEC
3M ESPE
593600/05-2018
Silica glass, polyacrylic acid
Dual polymerizing temporary resin cement
Harvard Implant semipermanent
HIS
Harvard Dental Intl
7206489/07-2014
Methacrylates, zinc oxide
Chemical polymerizing temporary cement
TempBond
TBO
Kerr
Dual polymerizing self-adhesive resin cement
Perma Cem 2.0
PC2
DMG GmbH
014894/12-2013
Ionomer glass in a bisphenol A diglycidylmethacrylate (Bis-GMA)-based matrix consisting of dental resins, activators and additives.
RelyX Unicem 2 Automix
RUN
3M ESPE
625709/10-2017
Phosphoric acid modified methacrylate monomers, bi-functional methacrylate, silanated fillers, initiator components, stabilizers, methacrylate monomers, alkaline fillers, pigments
Panavia SA
PSA
Kuraray Noritake Dental
6A0004/05-2016
10-Methacryloyloxydecyl dihydrogen phosphate (MDP), Bis-GMA, triethyleneglycol dimethacrylate (TEGDMA), hydrophobic aromatic dimethacrylate, silanated barium glass filler, silanated colloidal silica, dl-camphorquinone, benzoyl peroxide, initiators, hydrophobic aliphatic dimethacrylates, surface treated sodium fluoride, accelerators, pigments
Multilink Implant
MLI
Ivoclar Vivadent
S22243/11-2015
Dimethacrylate, 2-hydroxyethyl methacrylate (HEMA), barium glass, ytterbium trifluoride, spheroid mixed oxide
Multilink Automix
MLA
V11895/03-2018
Dimethacrylate, 2-hydroxyethyl methacrylate (HEMA), barium glass, ytterbium trifluoride, spheroid mixed oxide
Vita Adiva F-Cem
VAF
Vita Zahnfabrik
RelyX Ultimate
RUL
3M ESPE
Panavia F 2.0
PF2
Kuraray Noritake Dental
Panavia V5
Panavia 21
dual polymerizing adhesive resin cement
Chemical polymerizing adhesive resin cement
A 5554994/06-2017 B 5554985/06-2017
17601812/10-2017
Zinc oxide, eugenol
Methacrylates
607749/204-017
Methacrylate monomers, radiopaque, silanted fillers, initiator components, stabilizers, rheological additives, radiopaque alkaline fillers, pigments, fluorescence dye, dark cure activator for Scotchbond Universal adhesive
A 630066/03-2017 B 7A0013/03-2017
MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic aliphatic dimethacrylate, silanated silica filler, silanated colloidal silica, dl-campherquinone, catalysts, initiators, silanated barium glass filler, surface treated sodium fluoride, accelerators, pigments
PV5
AP0014/08-2018
Bisphenol A diglycidylmethacrylate (Bis-GMA), triethyleneglycol dimethacrylate (TEGDMA, hydrophobic aromatic dimethacrylate, hydrophilic aliphatic dimethacrylate, initiators, accelerators, silanated barium glass filler, silanated fluoroalminosilicate glass filler, colloidal silica, silanated aluminium oxide filler, dl-camphorquinone, pigments
P21
00674E/11-2013
MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, silanated silica filler, colloidal silica, catalysts, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic aliphatic dimethacrylate, silanated titanium oxide, silanated barium glass filler, catalysts, accelerators, pigments
Type 1 Type 2 Type 3
Figure 2. Illustration of crown fracture types of retention test. Type 0 represents no damage to crown. Figure 1. Custom tensile device for removing crowns from implant abutment surface.
Zwick/Roell) at a crosshead speed of 1 mm/min in a custom specimen holder (Fig. 1). The tensile crown retention force was recorded (textXpert v2.2; Zwick/ Roell). Fracture patterns of the crowns were evaluated by Rohr et al
a single individual (N.R.) and were classified as Type 0 (no fracture), Type 1 (small fracture at the cervical portion), Type 2 (crown completely separated through the cervical portion), and Type 3 (top portion of the crown separating, leaving the cervical portion adhering to the implant surface) (Fig. 2). THE JOURNAL OF PROSTHETIC DENTISTRY
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Table 2. Results of retention test and fracture types of polymer-infiltrated ceramic crowns on zirconia implants using different cements
Type
Code
Retention Force Without Primer (N)
Glass-ionomer cement
KEC
196 ±34A
Dual polymerizing temporary resin cement
HIS
43 ±6
Self polymerizing temporary cement
TBO
Dual polymerizing selfadhesive resin cement
Chemical polymerizing adhesive resin cement
Retention Force With Primer (N)
Fracture Type With Primer
Shear Bond Strength Without Primer (Mpa)
Shear Bond Strength With Primer (MPa)
Diametral Tensile Strength (MPa)
0
-
-
2.8 ±0.6A
-
8.4 ±1.5A
B
-
5.2 ±0.8A
0
-
-
0.0 ±0.0
127 ±15C
0
-
-
1.1 ±0.4B
-
1.4 ±0.2B
PC2
261 ±41D
2
-
-
5.3 ±0.7C
-
47.3 ±2.5C
RUN
253 ±15D
2
-
-
3.2 ±0.5A
-
PSA Dual polymerizing adhesive resin cement
B
Fracture Type Without Primer
270 ±26
D,E,a
A,D,a
MLA VAF RUL
2
470 ±67
A,b
2
4.1 ±0.5
A,C,a
7.2 ±1.9
35.8 ±5.2D,G
B,b
48.2 ±3.2C,E 51.3 ±1.7E,F
1
B,a
257 ±22
1/2
1.1 ±0.2
222 ±16A,D,a
1
243 ±29B,a
1/2
1.1 ±0.4B,a
5.7 ±1.5B,b
238 ±14A,D,a
1
269 ±36B,a
1/2
0.0 ±0.0B,a
3.1 ±1.5C,b
55.3 ±3.6F
245 ±16A,D,a
1
224 ±29B,a
1
3.2 ±0.3A,a
3.7 ±0.7C,a
33.7 ±3.7G
PF2
318 ±28E,a
2
363 ±59C,a
2
5.5 ±0.7C,a
5.7 ±0.7B,a
36.4 ±4.3D,G
PV5
D,a
1
B,a
2
B,a
MLI
P21
226 ±10
254 ±13
605 ±82
F
288 ±26
3
-
-
0.5 ±0.5
B,a
39.1 ±3.6D A,b
10.6 ±3.0
5.2 ±0.6
4.5 ±0.7
D
-
B,C,b
52.5 ±5.0F 36.6 ±3.7D,G
Statistically similar groups within 1 testing method marked in same column with superscript uppercase letters and same row in superscript lowercase letters.
The shear bond strength to sections of polished, embedded zirconia (Vita YZ; Vita Zahnfabrik) was measured for all cements (Table 1). The zirconia surface was polished in steps, down to 3-mm diamond paste (Ra=0.04 ±0.02 mm, n=3) to test the chemical bond of the cements to zirconia. The procedure of the Swiss shear test was used.37-39 Shear bond strength testing was performed for MLI, MLA, VAF, RUL, PSA, PF2, and PV5 cements with and without application of the respective ceramic primer. Six specimens were used for each test group. The zirconia specimens were fixed in a customized holding device. An acrylic resin cylinder (D+R Tec) with an inner diameter of 2.9 mm and height of 5 mm was fastened vertically on the zirconia surface. Cement was applied through the opening of the cylinder onto the surface. The cement was compressed with a headless steel screw with a force of 1 N. The cement was allowed to autopolymerize at room temperature. After 10 minutes, the specimens were removed from the holding device and stored in 37 C water for 24 hours. Downward vertical shear bond strength testing with a concave surface was performed at a crosshead speed of 1 mm/min using a universal testing machine (Z010; Zwick/Roell). The force at fracture was recorded (textXpert v2.2; Zwick/ Roell). After the strength measurements, the zirconia surfaces were polished and reused for the subsequent test series. The diametral tensile strength of all the cements was measured with cylindrical test specimens (3 mm in height and diameter) (n=10), made in Teflon molds. The cement was placed into the respective cavities of the Teflon mold and kept in place with a plastic foil and a glass plate on each side. After 1 hour’s storage in distilled water at
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37 C, the specimens were carefully removed from the mold and stored in water at 37 C for another 24 hours. The specimens were allowed to autopolymerize at room temperature. The specimens were loaded perpendicular to the cylinder axis until fracture at a crosshead speed of 1 mm/min (Z020, Zwick/Roell). The following equation was used to calculate diametral tensile strength:40
st =2F=pdh;
(1)
where st is the diametral tensile strength (MPa), F the fracture load (N), d the specimen diameter, and h the specimen height (mm). Data from each test parameter were tested for normality by the Shapiro-Wilk test. Statistical analysis was performed by 1- and 2-way (hypotheses 2, 4) analysis of variance (ANOVA) followed by post hoc comparison with the Fisher LSD test to determine differences between the retention force groups (a=.05). RESULTS The results for crown retention of all 13 cements on zirconia implants are displayed in Table 2. The retention force values were significantly influenced by the cement type applied (F(12)=84.6, P<.001). The observed fracture patterns (Fig. 2) for the different cements are presented in Table 2. No damage occurred to crowns cemented using HIS, TBO, or KEC (Type 0 failure). For MLI, MLA, VAF, RUL, and PV5, only small fractures at the cervical part of the crown were noted (Type 1 failure). Type 2 crown fractures were noted for PC2, RUN, PSA, and PF2 cements. For P21 cement, the top of the crown fractured while the cervical part remained on the implant (Type 3
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700.0
Retention Force (N)
600.0
P21
500.0
PSAp
400.0 300.0 200.0
VAFp
PV5 VAF
MLI MLA
PV5p PSA RUL
RUN KEC
RULp
TBO
100.0
2.0
MLIP
y = 5.1775x + 233.66 R2 = 0.24618
y = –5.9896x2 + 71.899x + 46.712 R2 = 0.99556
HIS
0.0 0.0
PF2p PF2 PC2 MLIp MLAp
y = –13.215x2 + 270.78x – 781.24 R2 = 0.97737
4.0
6.0
8.0
10.0
12.0
Shear Bond Strength (MPa) Figure 3. Correlation between retention force of polymer-infiltrated ceramic crowns and shear bond strength of corresponding cements. Cements with weak bonds to crown or implant surfaces indicated by gray circles; adhesive and self-adhesive resin cements demonstrating bond to crown material, blue circles; adhesive and self-adhesive resin cements demonstrating chemical bond to both crown and implant surfaces, orange circles. Primer application indicated by additional p at end of cement code.
failure). Cement was found to adhere mainly to the polymer-infiltrated ceramic site, except small particles that remained on the implant abutment retention grooves for some composite resin cements (MLI, MLA, VAF, PC2, RUN, RUL, PSA, PF2, and PV5). Residual cement material for HIS, TBO, and KEC could be easily removed from the intaglio of the crown. For P21 cement, cement residue was observed on the abutment and on the polymer-infiltrated ceramic. The retention force of crowns cemented with PSA was significantly increased when ceramic primer was applied on implant abutment and crown surfaces (Table 2), although 2-way ANOVA revealed no effect of the cement (F(6)=2.5, P=.145) or the use of primer (F(1)=3.6, P=.117) on the retention of the crowns. The change in crown retention strength when using ceramic primer with MLI, MLA, VAF, RUL, PF2, and PV5 was not statistically significant (P>.05) compared with those without the primer. Fracture patterns for RUL, PSA, and PF2 were similar to values obtained without ceramic primer. With application of ceramic primer, the fracture patterns of MLI, MLA, VAF, and PV5 cements shifted from Type 1 to Type 2 failure. For all specimens, adhesive failures occurred during the shear test (Table 2). Shear bond strength values differed significantly between the cements (F(12)=60.4, P<.001). The application of ceramic primer significantly increased the shear bond strength of MLI, MLA, VAF, PSA, and PV5 but not of RUL or PF2. The 2-way ANOVA revealed no significant effect of the cement (F(6)=3.2, P=.093) but of the primer (F(1)=18.1, P=.005). The results of the diametral tensile strength test differed Rohr et al
significantly from each other (F(12)=273.8, P<.001) and are listed in Table 2. A correlation between the retention force of the cemented, polymer-infiltrated ceramic crowns and the shear bond strength of the corresponding cements to zirconia is displayed in Fig. 3. Adhesive and self-adhesive composite resin cements with a shear bond strength to zirconia below 5.3 MPa are demarcated as blue circles in Fig. 3 and are located along a slightly increasing horizontal line. Statistically, no difference (P>.05) was found among the retention force values within this group when the post hoc test was used, except for PV5 with primer compared with RUL with primer. Adhesive and selfadhesive composite resin cements with higher shear bond strength values are provided as orange circles in Fig. 3. Their fracture pattern revealed an increasing retention force. These cements are aligned according to a polynomial function, generating a maximum value near 600 N. Temporary cements are identified as gray circles in Fig. 3. With increasing shear bond strength, values in this cement category approach the retention force values of adhesive and self-adhesive composite resin cements. No correlation was found between diametral tensile strength and retention force. DISCUSSION The first hypothesis that retention forces are higher for adhesive and self-adhesive cement than for temporary cements was confirmed. The second hypothesis that the application of primer on the crown and implant abutment increases retention forces was only confirmed for the self-adhesive cement PSA but rejected for all adhesive cements. That shear bond strength of adhesive and self-adhesive cements to zirconia is higher than for temporary cements was confirmed. That the application of primer on the zirconia surface increases the shear bond strength was only confirmed for MLI, MLA, VAF, PSA, and PV5. Because the diametral tensile strength varied significantly, the final hypothesis was also confirmed. Although it is difficult to achieve a sufficient bond to zirconia,21 the evaluated composite resin cements (MLI, MLA, VAF, PC2, RUN, RUL, PSA, PF2, PV5, and P21) displayed retention forces from 222 ±156 N (MLA) to 605 ±82 N (P21). Cements PC2, RUN, RUL, PSA, PF2, and P21 contain methacrylate monomers with phosphate groups, which are able to bond slightly to zirconia by phosphate groups.32 The cements MLI, MLA, VAF, and PV5 lack monomers with phosphate groups, although this did not significantly affect crown retention force, which might be due to a mechanical retention in the undercuts of the abutment or a tight fit of the polymerized cement layer on the abutment that may lead to a vacuum effect. Glass-ionomer (KEC) and zinc oxide THE JOURNAL OF PROSTHETIC DENTISTRY
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(TBO) cements are based on carboxyl groups, which provide weak bonds to zirconia. Therefore, these values were lower than those obtained using self-adhesive or adhesive composite resin cements (TBO, 127 ±15; KEC, 196 ±33 N). The temporary cement (HIS) demonstrated the lowest retention forces, possibly explained by the lack of any bonding agents, such as phosphate or carboxyl groups, in its composition. The results confirm previous findings with lithium disilicate crowns cemented to zirconia abutments, where P21 also revealed higher retention strength than RUN or KEC.36 The fracture patterns of the crowns were more pronounced with higher retention force. Especially high damage to the crowns was noted when using P21 (Type 3), which also attained the highest retention force values (605 ±82 N). No damage was found on crowns that were removed with a retention force below 200 N. Small cervical chipping fractures (Type 1) were recorded for removal forces between 200 and 250 N, and a separation of the crown at the cervical area (Type 2) occurred when forces were between 250 and 500 N. Crown fractures indicate that the crown material was weaker than the bond strength of the cement. Hence, the fracture load values of the crowns cemented with self-adhesive or adhesive composite resin cements were all above 200 N. These cements provide acceptable bond strengths using this test arrangement. Because the composite resin cement was mainly attached to the polymer-infiltrated crown material after testing, it can be concluded that for composite resin cements, primarily the bond to zirconia was evaluated in this test setup. The application of primer on crowns and abutments increased retention forces only for PSA. The Clearfil Ceramic Primer applied for PSA contains MDP and silane, which were responsible for increasing the retention force by forming strong chemical bonds. For VAF and PV5 cements, the application of primer did not significantly increase retention force. The MDP component in the primer provides a rather low pH that might inhibit cement polymerization. A buffer in the cement may be necessary to eliminate this disadvantage. An increase in retention force with ceramic primer application, which was not statistically different, was found for PF2, which contains MDP and hydrophilic aliphatic dimethacrylate. Therefore, a strong bond was already achieved without application of a ceramic primer. However, an increase in retention force for PF2 with a different primer treatment (PRIME plus; Bisco Inc) was recorded in another study, where zirconia crowns on zirconia abutments were tested.34 The primer applied contained organophosphate and a carboxylic acid monomer that may have interacted with the zirconia surface more so than hydroxyl groups.34 The highest shear bond strength was recorded for PF2 and P21, confirming results found in another study.18 THE JOURNAL OF PROSTHETIC DENTISTRY
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PSA, PF2, and P21 contain MDP. Phosphate-ester groups of this monomer are initially able to form a strong bond to zirconia.20 PF2 and P21 additionally contain a hydrophilic aliphatic dimethacrylate that may have added to their high bond strength. Because the chemical bond of MDP to zirconia partially degrades over months,15,41 in future studies, retention should be investigated after aging. The application of primer increased the shear bond strength values significantly for MLI, MLA, VAF, PSA, and PV5. For MLI and MLA, Monobond plus was applied, which contains a silane. The silane monomer is intended to form a chemical bond between hydrophilic zirconia and hydrophobic monomers of the cement. According to the shear bond test, a chemical bond was formed. However, it did not contribute to the retention force of these cements. For the application of Scotchbond Universal with RUL, neither the retention force nor the shear bond strength was significantly affected by the applied adhesive. Although Scotchbond universal contains silane, a significantly increased bond strength to glass was found when a silane coupling agent was applied on the surface before Scotchbond placement.42 The present study also supports these findings42 of insufficient effectiveness of the silane incorporated in the Scotchbond Universal adhesive. In contrast, the Clearfil Ceramic Primer that was applied for PSA, PV5, and Vita Adiva Zr-Prime for VAF contains MDP and silane, which increases the bonding capabilities to zirconia.20 The diametral tensile strengths of the cements did not seem to influence the retention mechanism. When crowns are cemented on an implant, 3 mechanisms are responsible for their retention, besides preparation form and crown fit. First, the rough surfaces of crowns and implants provide microretentive undercuts for the cement, thus causing mechanical interlocking. Second, a tight fit of the cement layer on the abutment and the intaglio surface of the crown may lead to a vacuum that has to be overcome in order to remove the crown. Third, a chemical bond to the ceramic can be achieved over hydroxyl groups34 or phosphate groups.17,20 Bonding to silicate ceramics by etching with hydrofluoric acid leading to an increase in surface area is considered standard procedure in dentistry.27,43 Establishing a microretentive structure on zirconia is difficult because of its resistance to hydrofluoric acid.21 As a result, special monomers that are able to bond with zirconia such as MDP have been developed to achieve a strong chemical bond. The chemical bond between cement and implant was evaluated using the shear bond test design. When correlating the results of the retention force test of the crowns to the shear bond strength, 3 groups were formed. First, temporary cement (HIS, TBO) and Rohr et al
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glass-ionomer cement (KEC) provide retention force values below 200 MPa to zirconia. Because these cements revealed low diametral tensile strengths, the cement can be considered the weakest factor of the reconstruction when the retention of the crowns is tested. Therefore, the cement is crushed during removal of the crown, reducing the vacuum effect. Retention force increased with the increasing shear bond strength of the cements. For this group, no damage was detected on the crowns. Self-adhesive and adhesive composite resin cements with good bonding capabilities to polymer-infiltrated ceramic and a weak bond to zirconia represent the second group. For these cements, higher forces of 220 to 290 N had to be applied to remove the crown, causing small crown fractures (type 1 and 2). The shear bond strength values and therefore the chemical bond for these cements varied between 0.0 and 5.3 MPa, although retention force values of the crowns were within a small range of 220 to 290 N. The strong bond to the etched polymer-infiltrated ceramic28 of self-adhesive and adhesive composite resin cements means that a higher vacuum effect is necessary to remove the crown. The vacuum effect that has to be eliminated is higher than the bonding force to zirconia for these cements, hence their retention force values are similar, regardless of their chemical bonding capabilities. The third group is represented by cements with high bonding capabilities to polymer-infiltrated ceramic and zirconia because of the cement properties themselves or the additional primer application. All of the cements in these groups form their bond to zirconia over MDP. The shear bond strength to zirconia for these cements is above 5.3 MPa. Because the chemical bond to zirconia in this group is higher than the vacuum effect necessary to remove the crown, retention force values for these cements also start to increase with the shear bond strength. The correlation between shear bond strength and crown retention force implies that a single shear bond strength test is not sufficient to estimate the clinical performance of dental cement. A crown retention test provides more information on the interaction between mechanical and chemical properties. Although the retention forces of crowns cemented with adhesive materials maintained by vacuum effect provided sufficient bond strength, the effect of aging and cyclic loading on the vacuum effect has to be further investigated. Clinical tests, or a cyclic loading approach, may demonstrate whether crowns that mainly adhere to the implant by vacuum effect can endure multidirectional chewing forces. In a clinical study6 no debonding of the crowns cemented to zirconia implants using RUN were reported. The present study investigated axial retention forces. In the oral environment, load transmission is far more complex, and further effects such as humidity and thermal stress affect the bonding to zirconia.15,41 The results Rohr et al
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of the present study should therefore be interpreted with caution. Nevertheless, the results provide a better understanding of how the bonding performance of the cement influences the crown retention force. CONCLUSIONS Within the limitations imposed by the current study, the following conclusions were drawn: 1. Retention forces were higher for adhesive and selfadhesive cement than for temporary cements. 2. The application of primer on the crown and implant abutment increased retention forces only for 1 selfadhesive cement (Panavia SA). 3. The shear bond strength of adhesive and selfadhesive cements to zirconia was not generally higher than for temporary cements. 4. The application of primer on the zirconia surface increased the shear bond strength for the selfadhesive cement Panavia SA and the adhesive cements Multilink Implant, Multilink Automix, Vita Adiva F-Cem, and Panavia V5. 5. The diametral tensile strength varied significantly among the cements. REFERENCES 1. Osman R, Swain M. A critical review of dental implant materials with an emphasis on titanium versus zirconia. Materials 2015;8:932-58. 2. Spies BC, Patzelt SB, Vach K, Kohal RJ. Monolithic lithium-disilicate single crowns supported by zirconia oral implants: three-year results of a prospective cohort study. Clin Oral Impl Res 2016;27:1160-8. 3. Gahlert M, Burtscher D, Pfundstein G, Grunert I, Kniha H, Roehling S. Dental zirconia implants up to three years in function: a retrospective clinical study and evaluation of prosthetic restorations and failures. Int J Oral Maxillofac Implants 2013;28:896-904. 4. Jung RE, Grohmann P, Sailer I, Steinhart YN, Féher A, Hämmerle C, et al. Evaluation of a one-piece ceramic implant used for single-tooth replacement and three-unit fixed partial dentures: a prospective cohort clinical trial. Clin Oral Implants Res 2016;27:751-61. 5. Spies BC, Stampf S, Kohal RJ. Evaluation of zirconia-based all-ceramic single crowns and fixed dental prosthesis on zirconia implants: 5-year results of a prospective cohort study. Clin Implant Dent Relat Res 2015;17:1014-28. 6. Spies BC, Kohal RJ, Balmer M, Vach K, Jung RE. Evaluation of zirconia-based posterior single crowns supported by zirconia implants: preliminary results of a prospective multicenter study. Clin Oral Implants Res 29 March 2016. http://dx.doi.org/10.1111/clr.12842. [ePub Ahead of Print]. 7. Coldea A, Swain MV, Thiel N. Hertzian contact response and damage tolerance of dental ceramics. J Mech Behav Biomed Mater 2014;34:124-33. 8. Rohr N, Coldea A, Zitzmann NU, Fischer J. Loading capacity of implant supported hybrid ceramic crowns. Dent Mater 2015;31:e279-88. 9. Groten M, Probster L. The influence of different cementation modes on the fracture resistance of feldspathic ceramic crowns. Int J Prosthodont 1997;10: 169-77. 10. Burke FJ, Fleming GJ, Nathanson D, Marquis PM. Are adhesive technologies needed to support ceramics? An assessment of the current evidence. J Adhes Dent 2002;4:7-22. 11. Kelly JR. Dental ceramics: current thinking and trends. Dent Clin North Am 2004;48:513-30. 12. Stawarczyk B, Beuer F, Ender A, Roos M, Edelhoff D, Wimmer T. Influence of cementation and cement type on the fracture load testing methodology of anterior crowns made of different materials. Dent Mater J 2013;30:888-95. 13. Atsu SS, Kilicarslan MA, Kucukesmen HC, Aka PS. Effect of zirconium-oxide ceramic surface treatments on the bond strength to adhesive resin. J Prosthet Dent 2006;95:430-6. 14. Yoshida K, Tsuo Y, Atsuta M. Bonding of dual-cured resin cement to zirconia ceramic using phosphate acid ester monomer and zirconate coupler. J Biomed Mater Res B Appl Biomater 2006;77:28-33.
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15. de Souza G, Hennig D, Aggarwal A, Tam LE. The use of MDP-based materials for bonding to zirconia. J Prosthet Dent 2014;112:895-902. 16. Tanıs¸ MÇ, Akçaboy C. Effects of different surface treatment methods and MDP monomer on resin cementation of zirconia ceramics an in vitro study. J Lasers Med Sci 2015;6:174-81. 17. Thompson JY, Stoner BR, Piascik JR, Smith R. Adhesion/cementation to zirconia and other non-silicate ceramics: where are we now? Dent Mater 2011;27:71-82. 18. Lüthy H, Loeffel O, Hammerle CH. Effect of thermocycling on bond strength of luting cements to zirconia ceramic. Dent Mater 2006;22:195-200. 19. Ozcan M, Nijhuis H, Valandro LF. Effect of various surface conditioning methods on the adhesion of dual-cure resin cement with MDP functional monomer to zirconia after thermal aging. Dent Mater J 2008;27:99-104. 20. Kern M, Wegner SM. Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 1998;14:64-71. 21. Mahmoodi N, Hooshmand T, Heidari S, Khoshro K. Effect of sandblasting, silica coating, and laser treatment on the microtensile bond strength of a dental zirconia ceramic to resin cements. Lasers Med Sci 2016;31:205-11. 22. Jardel V, Degrange M, Picard B, Derrien G. Correlation of topography to bond strength of etched ceramic. Int J Prosthodont 1999;12:59-64. 23. Blatz MB, Chiche G, Holst S, Sadan A. Influence of surface treatment and simulated aging on bond strengths of luting agents to zirconia. Quintessence Int 2007;38:745-53. 24. Nothdurft FP, Motter PJ, Pospiech PR. Effect of surface treatment on the initial bond strength of different luting cements to zirconium oxide ceramic. Clin Oral Investig 2009;13:229-35. 25. Li R, Zhou H, Wei W, Wang C, Sun YC, Gao P. Effects of mechanical and chemical pretreatments of zirconia or fiber posts on resin cement bonding. PLoS One 2015;10:e0129690. 26. Otani A, Amaral M, May LG, Cesar PF, Valandro LF. A critical evaluation of bond strength tests for the assessment of bonding to Y-TZP. Dent Mater 2015;31:648-56. 27. Blatz MB, Sadan A, Kern M. Resin-ceramic bonding: a review of the literature. J Prosthet Dent 2003;89:268-74. 28. Hu M, Weiger R, Fischer J. Comparison of two test designs for evaluating the shear bond strength of resin composite cements. Dent Mater 2016;32:223-32. 29. Van Noort R, Noroozi S, Howard IC, Cardew G. A critique of bond strength measurements. J Dent 1989;17:61-7. 30. DeHoff PH, Anusavice KJ, Wang Z. Three-dimensional finite element analysis of the shear bond test. Dent Mater 1995;11:126-31. 31. Sudsangiam S, van Noort R. Do dentin bond strength tests serve a useful purpose? J Adhes Dent 1999;1:57-67. 32. Heintze SD. Clinical relevance of tests on bond strength, microleakage and marginal adaptation. Dent Mater 2013;29:59-84. 33. Heintze SD. Crown pull-off test (crown retention test) to evaluate the bonding effectiveness of luting agents. Dent Mater 2010;26:193-206. 34. Kim SM, Yoon JY, Lee MH, Oh NS. The effect of resin cements and primer on retentive force of zirconia copings bonded to zirconia abutments with insufficient retention. J Adv Prosthodont 2013;5:198-203.
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35. Nematollahi F, Beyabanaki E, Alikhasi M. Cement selection for cementretained implant-supported prostheses: a literature review. J Prosthodont 2016;25:599-606. 36. Sellers K, Powers JM, Kiat-Amnuay S. Retentive strength of implantsupported CAD-CAM lithium disilicate crowns on zirconia custom abutments using 6 different cements. J Prosthet Dent 2017;117:247-52. 37. Holderegger C, Sailer I, Schuhmacher C, Schläpfer R, Hämmerle C, Fischer J. Shear bond strength of resin cements to human dentin. Dent Mater 2008;24: 944-50. 38. Stawarczyk B, Hartmann R, Hartmann L, Roos M, Özcan M, Sailer I, et al. The effect of dentin desensitizer on shear bond strength of conventional and self-adhesive resin luting cements after aging. Oper Dent 2011;36:492-501. 39. Bähr N, Keul C, Edelhoff D, Eichberger M, Roos M, Gernet W, et al. Effect of different adhesives combined with two resin composite cements on shear bond strength to polymeric CAD/CAM materials. Dent Mater J 2013;32: 492-501. 40. Blumer L, Schmidli F, Weiger R, Fischer J. A systematic approach to standardize artificial aging of resin composite cements. Dent Mater 2015;31: 855-63. 41. Wolfart M, Lehmann F, Wolfart S, Kern M. Durability of the resin bond strength to zirconia ceramic after using different surface conditioning methods. Dent Mater 2007;23:45-50. 42. Yoshihara K, Nagaoka N, Sonoda A, Maruo Y, Makita Y, Okihara T, et al. Effectiveness and stability of silane coupling agent incorporated in “universal” adhesives. Dent Mater 2016;32:1218-25. 43. Matinlinna JP, Vallittu PK. Bonding of resin composites to etchable ceramic surfaces-an insight review of the chemical aspects on surface conditioning. J Oral Rehabil 2007;34:622-30. Corresponding author: Dr Nadja Rohr Division of Dental Materials and Engineering Department of Reconstructive Dentistry and Temporomandibular Disorders University Center for Dental Medicine University of Basel Hebelstrasse 3 CH-4056 Basel SWITZERLAND Email: [email protected] Acknowledgments The authors thank Vita Zahnfabrik, Bad Säckingen, Germany, for supporting this study with materials. Copyright © 2017 The Authors. Published by Elsevier Inc. on behalf of the Editorial Council for The Journal of Prosthetic Dentistry. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).
Rohr et al
Influence of cement type and ceramic primer on retention of polymer-infiltrated ceramic crowns to a one-piece zirconia implant Nadja Rohr, Dr med dent,a Stefan Brunner, Dr med dent,b Sabrina Märtin,c and Jens Fischer, Prof Dr med dent, Dr rer natd
ABSTRACT Statement of problem. The best procedure for cementing a restoration to zirconia implants has not yet been established. Purpose. The purpose of this in vitro study was to measure the retention of polymer-infiltrated ceramic crowns to zirconia 1-piece implants using a wide range of cements. The effect of ceramic primer treatment on the retention force was also recorded. The retention results were correlated with the shear bond strength of the cement to zirconia and the indirect tensile strength of the cements to better understand the retention mechanism. Material and methods. The retention test was performed using 100 polymer-infiltrated ceramic crowns (Vita Enamic) and zirconia implants (ceramic.implant CI) The crowns were cemented with either temporary cement (Harvard Implant semipermanent, Temp Bond), glass-ionomer cement (Ketac Cem), self-adhesive cement (Perma Cem 2.0, RelyX Unicem Automix 2, Panavia SA), or adhesive cement (Multilink Implant, Multilink Automix, Vita Adiva F-Cem, RelyX Ultimate, Panavia F 2.0, Panavia V5 or Panavia 21) (n=5). Additionally ceramic primer was applied on the intaglio crown surface and implant abutment before cementation for all adhesive cements (Multilink Implant, Multilink Automix: Monobond plus; RelyX Ultimate Scotchbond Universal; Vita Adiva F-Cem: Vita Adiva Zr-Prime; Panavia F2.0, Panavia V5: Clearfil Ceramic Primer) and 1 self-adhesive cement containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP) (Panavia SA: Clearfil Ceramic Primer). Crown debond fracture patterns were recorded. Shear bond strength was determined for the respective cement groups to polished zirconia (n=6). The diametral tensile strength of the cements was measured (n=10). Statistical analysis was performed using 1-way or 2-way analysis of variance followed by the Fisher LSD test (a=.05) within each test parameter. Results. Adhesive and self-adhesive resin cements had shear bond strength values of 0.0 to 5.3 MPa and revealed similar retention forces. Cements containing MDP demonstrated shear bond strength values above 5.3 MPa and displayed increased retention. The highest retention values were recorded for Panavia F 2.0 (318 ±28 N) and Panavia 21 (605 ±82 N). All other adhesive and self-adhesive resin cements attained retention values between 222 ±16 N (Multilink Automix) and 270 ±26 N (Panavia SA), which were significantly higher (P<.05) than glassionomer (Ketac Cem: 196 ±34 N) or temporary cement (Harvard Implant semipermanent: 43 ±6 N, Temp Bond: 127 ±13 N). Application of manufacturer-specific ceramic primer increased crown retention significantly only for Panavia SA. Conclusions. Products containing MDP provided a high chemical bond to zirconia. Self-adhesive and adhesive resin cements with low chemical bonding capabilities to zirconia provided retention force values within a small range (220 to 290 N). (J Prosthet Dent 2017;-:---)
Implants made from zirconia are a promising alternative to the well-established titanium implants.1-4 However, when restored with zirconia crowns, chipping of the veneering ceramic has been recorded.5,6 An optimal
material for creating a restoration on zirconia implants has not yet been established. Materials with a low elastic modulus, such as polymer-infiltrated ceramic,7 might be able to buffer intraoral forces on the zirconia implant.
a
Postdoctoral student, Division of Dental Materials and Engineering, Department of Reconstructive Dentistry and Temporomandibular Disorders, University Center for Dental Medicine Basel, University of Basel, Basel, Switzerland. Private practice, Langenthal, Switzerland. c Laboratory Manager, Vita Zahnfabrik, Bad Säckingen, Germany. d Professor, Division of Dental Materials and Engineering, Department of Reconstructive Dentistry and Temporomandibular Disorders, University Center for Dental Medicine Basel, University of Basel, Basel, Switzerland. b
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Clinical Implications Self-adhesive and adhesive composite resin cements with only slight bonding capabilities to zirconia still achieve high crown retention. The use of a primer on the implant abutment affected the retention force of the crown only for Panavia SA.
Polymer-infiltrated ceramic shows slightly higher fracture load values than does feldspathic ceramic when used on zirconia.8 Zirconia implants are currently offered as 1-piece devices. Therefore, a restoration has to be cemented directly on the implant. The choice of the cement connecting crown and implant greatly relies on the restorative material used. For silica and polymer-infiltrated ceramics, cements with a high compressive strength such as adhesive resin cements are recommended to increase the fracture load of the system.8-12 Fracture load values of oxide ceramics are not influenced by cement type.12 However, cementation of oxide ceramic restorations with resin-based materials can improve their marginal adaptation.10 The application of 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing bonding agents can increase bond strength to zirconia13-18 because of an interaction between the hydroxyl groups of MDP and the cationic surface of zirconia.19,20 Establishing a microretentive structure on zirconia is difficult because zirconia, with its high crystalline content without any silica phase, is resistant to hydrofluoric acid etching.21 The effect of silanization on establishing a chemical bond between the hydrophilic zirconia surface and the hydrophobic resin cement remains controversial.13,21-25 Bond strength is measured using various methods each using macro- or microspecimens: shear tests, tensile tests, or push-out tests.26-28 The bond strength of resin cements to zirconia varies significantly according to the test design.26,28 The variability in results among these testing methods makes it difficult to establish a correlation between laboratory data and the clinical performance of tested materials.29-32 A more clinically related method of testing the retention capability of dental cement is the crown retention test design, where crowns are cemented under a defined load and pulled off in an axial direction after the cement has set.33-36 Thus, the purpose of this study was to evaluate the retention of polymer-infiltrated ceramic crowns on zirconia implants using a wide range of commercially available cement types. The interaction between the tensile retention and the shear bond strength of cements to zirconia, as well as their diametral tensile strengths, were evaluated. The effect of manufacturer-specific
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ceramic primer surface treatments on retention forces and shear bond strengths were additionally tested. The 5 hypotheses were that retention forces are higher for adhesive and self-adhesive cement than for temporary cements; that the application of primer on the crown and implant abutment increases retention forces; that shear bond strength of adhesive and self-adhesive cements to zirconia is higher than for temporary cements; that the application of primer on the zirconia surface increases the shear bond strength; and that diametral tensile strength of the cements differs significantly. MATERIAL AND METHODS For the retention test, 100 zirconia implants (ceramic.implant CI, vitaclinical; Vita Zahnfabrik) 4.5 mm in diameter were used. The roughness of the abutment surface was Ra=0.42 ±0.06 mm (n=3) (T1000/TKK50, Hommelwerke). The endosseous portions of the implants were embedded in epoxy resin (Araldite, RenCast CW20/Ren HY49; Bodo Müller Chemie) according to ISO 14801:2016 Dentistry-Implants-Dynamic loading test for endosseous dental implants. All implants had an endosseous length of 10 mm and were inserted with a 3 mm clearance between the implant neck and resin surface. One implant was scanned with an optical scanner (inEos Blue; Dentsply Sirona). A mandibular right first molar crown was designed (inLab SW4.0; Dentsply Sirona). One hundred polymer-infiltrated ceramic crowns (Vita Enamic; Vita Zahnfabrik) were milled (inLab MCXL; Dentsply Sirona). All crowns and implants were cleaned in a 96% ethanol ultrasonic bath for 4 minutes (TPC-15; Telsonic). The intaglio surface of each crown was etched with hydrofluoric acid (Ceramics Etch; Vita Zahnfabrik) for 60 seconds. Sixty-five crowns were cemented on the implants using 13 different cements according to the manufacturers’ recommendations (Table 1) (n=5). The cements were selected to cover a wide range of cement classifications, compositions, and manufacturers. Additionally, 35 crowns were cemented on implants with adhesive cements MLI, MLA, VAF, PF2, and PV5 and 1 self-adhesive cement with MDP (PSA) using ceramic primer on the intaglio surface of the crown and implant abutment (MLI, MLA: Monobond plus, Ivoclar Vivadent; RUL: Scotchbond Universal, 3MEspe; VAF: Vita Adiva Zr-Prime, Vita; PSA, PF2, PV5: Clearfil Ceramic Primer, Kuraray) (n=5). The crowns were filled with cement, placed on the implants, and loaded with 25 N for 10 minutes at room temperature. They were not light polymerized; all materials were allowed to autopolymerize. Excess cement was eliminated using foam pellets. After the cementation process, the specimens were stored in distilled water at 37 C for 24 hours. The crown retention testing was performed using a universal testing machine (Z020;
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Table 1. Cement materials and ceramic primer used Type
Cement
Code
Manufacturer
Lot No/Exp Date
Composition
Glass-ionomer cement
Ketac Cem
KEC
3M ESPE
593600/05-2018
Silica glass, polyacrylic acid
Dual polymerizing temporary resin cement
Harvard Implant semipermanent
HIS
Harvard Dental Intl
7206489/07-2014
Methacrylates, zinc oxide
Chemical polymerizing temporary cement
TempBond
TBO
Kerr
Dual polymerizing self-adhesive resin cement
Perma Cem 2.0
PC2
DMG GmbH
014894/12-2013
Ionomer glass in a bisphenol A diglycidylmethacrylate (Bis-GMA)-based matrix consisting of dental resins, activators and additives.
RelyX Unicem 2 Automix
RUN
3M ESPE
625709/10-2017
Phosphoric acid modified methacrylate monomers, bi-functional methacrylate, silanated fillers, initiator components, stabilizers, methacrylate monomers, alkaline fillers, pigments
Panavia SA
PSA
Kuraray Noritake Dental
6A0004/05-2016
10-Methacryloyloxydecyl dihydrogen phosphate (MDP), Bis-GMA, triethyleneglycol dimethacrylate (TEGDMA), hydrophobic aromatic dimethacrylate, silanated barium glass filler, silanated colloidal silica, dl-camphorquinone, benzoyl peroxide, initiators, hydrophobic aliphatic dimethacrylates, surface treated sodium fluoride, accelerators, pigments
Multilink Implant
MLI
Ivoclar Vivadent
S22243/11-2015
Dimethacrylate, 2-hydroxyethyl methacrylate (HEMA), barium glass, ytterbium trifluoride, spheroid mixed oxide
Multilink Automix
MLA
V11895/03-2018
Dimethacrylate, 2-hydroxyethyl methacrylate (HEMA), barium glass, ytterbium trifluoride, spheroid mixed oxide
Vita Adiva F-Cem
VAF
Vita Zahnfabrik
RelyX Ultimate
RUL
3M ESPE
Panavia F 2.0
PF2
Kuraray Noritake Dental
Panavia V5
Panavia 21
dual polymerizing adhesive resin cement
Chemical polymerizing adhesive resin cement
A 5554994/06-2017 B 5554985/06-2017
17601812/10-2017
Zinc oxide, eugenol
Methacrylates
607749/204-017
Methacrylate monomers, radiopaque, silanted fillers, initiator components, stabilizers, rheological additives, radiopaque alkaline fillers, pigments, fluorescence dye, dark cure activator for Scotchbond Universal adhesive
A 630066/03-2017 B 7A0013/03-2017
MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic aliphatic dimethacrylate, silanated silica filler, silanated colloidal silica, dl-campherquinone, catalysts, initiators, silanated barium glass filler, surface treated sodium fluoride, accelerators, pigments
PV5
AP0014/08-2018
Bisphenol A diglycidylmethacrylate (Bis-GMA), triethyleneglycol dimethacrylate (TEGDMA, hydrophobic aromatic dimethacrylate, hydrophilic aliphatic dimethacrylate, initiators, accelerators, silanated barium glass filler, silanated fluoroalminosilicate glass filler, colloidal silica, silanated aluminium oxide filler, dl-camphorquinone, pigments
P21
00674E/11-2013
MDP, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, silanated silica filler, colloidal silica, catalysts, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic dimethacrylate, hydrophilic aliphatic dimethacrylate, silanated titanium oxide, silanated barium glass filler, catalysts, accelerators, pigments
Type 1 Type 2 Type 3
Figure 2. Illustration of crown fracture types of retention test. Type 0 represents no damage to crown. Figure 1. Custom tensile device for removing crowns from implant abutment surface.
Zwick/Roell) at a crosshead speed of 1 mm/min in a custom specimen holder (Fig. 1). The tensile crown retention force was recorded (textXpert v2.2; Zwick/ Roell). Fracture patterns of the crowns were evaluated by Rohr et al
a single individual (N.R.) and were classified as Type 0 (no fracture), Type 1 (small fracture at the cervical portion), Type 2 (crown completely separated through the cervical portion), and Type 3 (top portion of the crown separating, leaving the cervical portion adhering to the implant surface) (Fig. 2). THE JOURNAL OF PROSTHETIC DENTISTRY
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Table 2. Results of retention test and fracture types of polymer-infiltrated ceramic crowns on zirconia implants using different cements
Type
Code
Retention Force Without Primer (N)
Glass-ionomer cement
KEC
196 ±34A
Dual polymerizing temporary resin cement
HIS
43 ±6
Self polymerizing temporary cement
TBO
Dual polymerizing selfadhesive resin cement
Chemical polymerizing adhesive resin cement
Retention Force With Primer (N)
Fracture Type With Primer
Shear Bond Strength Without Primer (Mpa)
Shear Bond Strength With Primer (MPa)
Diametral Tensile Strength (MPa)
0
-
-
2.8 ±0.6A
-
8.4 ±1.5A
B
-
5.2 ±0.8A
0
-
-
0.0 ±0.0
127 ±15C
0
-
-
1.1 ±0.4B
-
1.4 ±0.2B
PC2
261 ±41D
2
-
-
5.3 ±0.7C
-
47.3 ±2.5C
RUN
253 ±15D
2
-
-
3.2 ±0.5A
-
PSA Dual polymerizing adhesive resin cement
B
Fracture Type Without Primer
270 ±26
D,E,a
A,D,a
MLA VAF RUL
2
470 ±67
A,b
2
4.1 ±0.5
A,C,a
7.2 ±1.9
35.8 ±5.2D,G
B,b
48.2 ±3.2C,E 51.3 ±1.7E,F
1
B,a
257 ±22
1/2
1.1 ±0.2
222 ±16A,D,a
1
243 ±29B,a
1/2
1.1 ±0.4B,a
5.7 ±1.5B,b
238 ±14A,D,a
1
269 ±36B,a
1/2
0.0 ±0.0B,a
3.1 ±1.5C,b
55.3 ±3.6F
245 ±16A,D,a
1
224 ±29B,a
1
3.2 ±0.3A,a
3.7 ±0.7C,a
33.7 ±3.7G
PF2
318 ±28E,a
2
363 ±59C,a
2
5.5 ±0.7C,a
5.7 ±0.7B,a
36.4 ±4.3D,G
PV5
D,a
1
B,a
2
B,a
MLI
P21
226 ±10
254 ±13
605 ±82
F
288 ±26
3
-
-
0.5 ±0.5
B,a
39.1 ±3.6D A,b
10.6 ±3.0
5.2 ±0.6
4.5 ±0.7
D
-
B,C,b
52.5 ±5.0F 36.6 ±3.7D,G
Statistically similar groups within 1 testing method marked in same column with superscript uppercase letters and same row in superscript lowercase letters.
The shear bond strength to sections of polished, embedded zirconia (Vita YZ; Vita Zahnfabrik) was measured for all cements (Table 1). The zirconia surface was polished in steps, down to 3-mm diamond paste (Ra=0.04 ±0.02 mm, n=3) to test the chemical bond of the cements to zirconia. The procedure of the Swiss shear test was used.37-39 Shear bond strength testing was performed for MLI, MLA, VAF, RUL, PSA, PF2, and PV5 cements with and without application of the respective ceramic primer. Six specimens were used for each test group. The zirconia specimens were fixed in a customized holding device. An acrylic resin cylinder (D+R Tec) with an inner diameter of 2.9 mm and height of 5 mm was fastened vertically on the zirconia surface. Cement was applied through the opening of the cylinder onto the surface. The cement was compressed with a headless steel screw with a force of 1 N. The cement was allowed to autopolymerize at room temperature. After 10 minutes, the specimens were removed from the holding device and stored in 37 C water for 24 hours. Downward vertical shear bond strength testing with a concave surface was performed at a crosshead speed of 1 mm/min using a universal testing machine (Z010; Zwick/Roell). The force at fracture was recorded (textXpert v2.2; Zwick/ Roell). After the strength measurements, the zirconia surfaces were polished and reused for the subsequent test series. The diametral tensile strength of all the cements was measured with cylindrical test specimens (3 mm in height and diameter) (n=10), made in Teflon molds. The cement was placed into the respective cavities of the Teflon mold and kept in place with a plastic foil and a glass plate on each side. After 1 hour’s storage in distilled water at
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37 C, the specimens were carefully removed from the mold and stored in water at 37 C for another 24 hours. The specimens were allowed to autopolymerize at room temperature. The specimens were loaded perpendicular to the cylinder axis until fracture at a crosshead speed of 1 mm/min (Z020, Zwick/Roell). The following equation was used to calculate diametral tensile strength:40
st =2F=pdh;
(1)
where st is the diametral tensile strength (MPa), F the fracture load (N), d the specimen diameter, and h the specimen height (mm). Data from each test parameter were tested for normality by the Shapiro-Wilk test. Statistical analysis was performed by 1- and 2-way (hypotheses 2, 4) analysis of variance (ANOVA) followed by post hoc comparison with the Fisher LSD test to determine differences between the retention force groups (a=.05). RESULTS The results for crown retention of all 13 cements on zirconia implants are displayed in Table 2. The retention force values were significantly influenced by the cement type applied (F(12)=84.6, P<.001). The observed fracture patterns (Fig. 2) for the different cements are presented in Table 2. No damage occurred to crowns cemented using HIS, TBO, or KEC (Type 0 failure). For MLI, MLA, VAF, RUL, and PV5, only small fractures at the cervical part of the crown were noted (Type 1 failure). Type 2 crown fractures were noted for PC2, RUN, PSA, and PF2 cements. For P21 cement, the top of the crown fractured while the cervical part remained on the implant (Type 3
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5
700.0
Retention Force (N)
600.0
P21
500.0
PSAp
400.0 300.0 200.0
VAFp
PV5 VAF
MLI MLA
PV5p PSA RUL
RUN KEC
RULp
TBO
100.0
2.0
MLIP
y = 5.1775x + 233.66 R2 = 0.24618
y = –5.9896x2 + 71.899x + 46.712 R2 = 0.99556
HIS
0.0 0.0
PF2p PF2 PC2 MLIp MLAp
y = –13.215x2 + 270.78x – 781.24 R2 = 0.97737
4.0
6.0
8.0
10.0
12.0
Shear Bond Strength (MPa) Figure 3. Correlation between retention force of polymer-infiltrated ceramic crowns and shear bond strength of corresponding cements. Cements with weak bonds to crown or implant surfaces indicated by gray circles; adhesive and self-adhesive resin cements demonstrating bond to crown material, blue circles; adhesive and self-adhesive resin cements demonstrating chemical bond to both crown and implant surfaces, orange circles. Primer application indicated by additional p at end of cement code.
failure). Cement was found to adhere mainly to the polymer-infiltrated ceramic site, except small particles that remained on the implant abutment retention grooves for some composite resin cements (MLI, MLA, VAF, PC2, RUN, RUL, PSA, PF2, and PV5). Residual cement material for HIS, TBO, and KEC could be easily removed from the intaglio of the crown. For P21 cement, cement residue was observed on the abutment and on the polymer-infiltrated ceramic. The retention force of crowns cemented with PSA was significantly increased when ceramic primer was applied on implant abutment and crown surfaces (Table 2), although 2-way ANOVA revealed no effect of the cement (F(6)=2.5, P=.145) or the use of primer (F(1)=3.6, P=.117) on the retention of the crowns. The change in crown retention strength when using ceramic primer with MLI, MLA, VAF, RUL, PF2, and PV5 was not statistically significant (P>.05) compared with those without the primer. Fracture patterns for RUL, PSA, and PF2 were similar to values obtained without ceramic primer. With application of ceramic primer, the fracture patterns of MLI, MLA, VAF, and PV5 cements shifted from Type 1 to Type 2 failure. For all specimens, adhesive failures occurred during the shear test (Table 2). Shear bond strength values differed significantly between the cements (F(12)=60.4, P<.001). The application of ceramic primer significantly increased the shear bond strength of MLI, MLA, VAF, PSA, and PV5 but not of RUL or PF2. The 2-way ANOVA revealed no significant effect of the cement (F(6)=3.2, P=.093) but of the primer (F(1)=18.1, P=.005). The results of the diametral tensile strength test differed Rohr et al
significantly from each other (F(12)=273.8, P<.001) and are listed in Table 2. A correlation between the retention force of the cemented, polymer-infiltrated ceramic crowns and the shear bond strength of the corresponding cements to zirconia is displayed in Fig. 3. Adhesive and self-adhesive composite resin cements with a shear bond strength to zirconia below 5.3 MPa are demarcated as blue circles in Fig. 3 and are located along a slightly increasing horizontal line. Statistically, no difference (P>.05) was found among the retention force values within this group when the post hoc test was used, except for PV5 with primer compared with RUL with primer. Adhesive and selfadhesive composite resin cements with higher shear bond strength values are provided as orange circles in Fig. 3. Their fracture pattern revealed an increasing retention force. These cements are aligned according to a polynomial function, generating a maximum value near 600 N. Temporary cements are identified as gray circles in Fig. 3. With increasing shear bond strength, values in this cement category approach the retention force values of adhesive and self-adhesive composite resin cements. No correlation was found between diametral tensile strength and retention force. DISCUSSION The first hypothesis that retention forces are higher for adhesive and self-adhesive cement than for temporary cements was confirmed. The second hypothesis that the application of primer on the crown and implant abutment increases retention forces was only confirmed for the self-adhesive cement PSA but rejected for all adhesive cements. That shear bond strength of adhesive and self-adhesive cements to zirconia is higher than for temporary cements was confirmed. That the application of primer on the zirconia surface increases the shear bond strength was only confirmed for MLI, MLA, VAF, PSA, and PV5. Because the diametral tensile strength varied significantly, the final hypothesis was also confirmed. Although it is difficult to achieve a sufficient bond to zirconia,21 the evaluated composite resin cements (MLI, MLA, VAF, PC2, RUN, RUL, PSA, PF2, PV5, and P21) displayed retention forces from 222 ±156 N (MLA) to 605 ±82 N (P21). Cements PC2, RUN, RUL, PSA, PF2, and P21 contain methacrylate monomers with phosphate groups, which are able to bond slightly to zirconia by phosphate groups.32 The cements MLI, MLA, VAF, and PV5 lack monomers with phosphate groups, although this did not significantly affect crown retention force, which might be due to a mechanical retention in the undercuts of the abutment or a tight fit of the polymerized cement layer on the abutment that may lead to a vacuum effect. Glass-ionomer (KEC) and zinc oxide THE JOURNAL OF PROSTHETIC DENTISTRY
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(TBO) cements are based on carboxyl groups, which provide weak bonds to zirconia. Therefore, these values were lower than those obtained using self-adhesive or adhesive composite resin cements (TBO, 127 ±15; KEC, 196 ±33 N). The temporary cement (HIS) demonstrated the lowest retention forces, possibly explained by the lack of any bonding agents, such as phosphate or carboxyl groups, in its composition. The results confirm previous findings with lithium disilicate crowns cemented to zirconia abutments, where P21 also revealed higher retention strength than RUN or KEC.36 The fracture patterns of the crowns were more pronounced with higher retention force. Especially high damage to the crowns was noted when using P21 (Type 3), which also attained the highest retention force values (605 ±82 N). No damage was found on crowns that were removed with a retention force below 200 N. Small cervical chipping fractures (Type 1) were recorded for removal forces between 200 and 250 N, and a separation of the crown at the cervical area (Type 2) occurred when forces were between 250 and 500 N. Crown fractures indicate that the crown material was weaker than the bond strength of the cement. Hence, the fracture load values of the crowns cemented with self-adhesive or adhesive composite resin cements were all above 200 N. These cements provide acceptable bond strengths using this test arrangement. Because the composite resin cement was mainly attached to the polymer-infiltrated crown material after testing, it can be concluded that for composite resin cements, primarily the bond to zirconia was evaluated in this test setup. The application of primer on crowns and abutments increased retention forces only for PSA. The Clearfil Ceramic Primer applied for PSA contains MDP and silane, which were responsible for increasing the retention force by forming strong chemical bonds. For VAF and PV5 cements, the application of primer did not significantly increase retention force. The MDP component in the primer provides a rather low pH that might inhibit cement polymerization. A buffer in the cement may be necessary to eliminate this disadvantage. An increase in retention force with ceramic primer application, which was not statistically different, was found for PF2, which contains MDP and hydrophilic aliphatic dimethacrylate. Therefore, a strong bond was already achieved without application of a ceramic primer. However, an increase in retention force for PF2 with a different primer treatment (PRIME plus; Bisco Inc) was recorded in another study, where zirconia crowns on zirconia abutments were tested.34 The primer applied contained organophosphate and a carboxylic acid monomer that may have interacted with the zirconia surface more so than hydroxyl groups.34 The highest shear bond strength was recorded for PF2 and P21, confirming results found in another study.18 THE JOURNAL OF PROSTHETIC DENTISTRY
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PSA, PF2, and P21 contain MDP. Phosphate-ester groups of this monomer are initially able to form a strong bond to zirconia.20 PF2 and P21 additionally contain a hydrophilic aliphatic dimethacrylate that may have added to their high bond strength. Because the chemical bond of MDP to zirconia partially degrades over months,15,41 in future studies, retention should be investigated after aging. The application of primer increased the shear bond strength values significantly for MLI, MLA, VAF, PSA, and PV5. For MLI and MLA, Monobond plus was applied, which contains a silane. The silane monomer is intended to form a chemical bond between hydrophilic zirconia and hydrophobic monomers of the cement. According to the shear bond test, a chemical bond was formed. However, it did not contribute to the retention force of these cements. For the application of Scotchbond Universal with RUL, neither the retention force nor the shear bond strength was significantly affected by the applied adhesive. Although Scotchbond universal contains silane, a significantly increased bond strength to glass was found when a silane coupling agent was applied on the surface before Scotchbond placement.42 The present study also supports these findings42 of insufficient effectiveness of the silane incorporated in the Scotchbond Universal adhesive. In contrast, the Clearfil Ceramic Primer that was applied for PSA, PV5, and Vita Adiva Zr-Prime for VAF contains MDP and silane, which increases the bonding capabilities to zirconia.20 The diametral tensile strengths of the cements did not seem to influence the retention mechanism. When crowns are cemented on an implant, 3 mechanisms are responsible for their retention, besides preparation form and crown fit. First, the rough surfaces of crowns and implants provide microretentive undercuts for the cement, thus causing mechanical interlocking. Second, a tight fit of the cement layer on the abutment and the intaglio surface of the crown may lead to a vacuum that has to be overcome in order to remove the crown. Third, a chemical bond to the ceramic can be achieved over hydroxyl groups34 or phosphate groups.17,20 Bonding to silicate ceramics by etching with hydrofluoric acid leading to an increase in surface area is considered standard procedure in dentistry.27,43 Establishing a microretentive structure on zirconia is difficult because of its resistance to hydrofluoric acid.21 As a result, special monomers that are able to bond with zirconia such as MDP have been developed to achieve a strong chemical bond. The chemical bond between cement and implant was evaluated using the shear bond test design. When correlating the results of the retention force test of the crowns to the shear bond strength, 3 groups were formed. First, temporary cement (HIS, TBO) and Rohr et al
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glass-ionomer cement (KEC) provide retention force values below 200 MPa to zirconia. Because these cements revealed low diametral tensile strengths, the cement can be considered the weakest factor of the reconstruction when the retention of the crowns is tested. Therefore, the cement is crushed during removal of the crown, reducing the vacuum effect. Retention force increased with the increasing shear bond strength of the cements. For this group, no damage was detected on the crowns. Self-adhesive and adhesive composite resin cements with good bonding capabilities to polymer-infiltrated ceramic and a weak bond to zirconia represent the second group. For these cements, higher forces of 220 to 290 N had to be applied to remove the crown, causing small crown fractures (type 1 and 2). The shear bond strength values and therefore the chemical bond for these cements varied between 0.0 and 5.3 MPa, although retention force values of the crowns were within a small range of 220 to 290 N. The strong bond to the etched polymer-infiltrated ceramic28 of self-adhesive and adhesive composite resin cements means that a higher vacuum effect is necessary to remove the crown. The vacuum effect that has to be eliminated is higher than the bonding force to zirconia for these cements, hence their retention force values are similar, regardless of their chemical bonding capabilities. The third group is represented by cements with high bonding capabilities to polymer-infiltrated ceramic and zirconia because of the cement properties themselves or the additional primer application. All of the cements in these groups form their bond to zirconia over MDP. The shear bond strength to zirconia for these cements is above 5.3 MPa. Because the chemical bond to zirconia in this group is higher than the vacuum effect necessary to remove the crown, retention force values for these cements also start to increase with the shear bond strength. The correlation between shear bond strength and crown retention force implies that a single shear bond strength test is not sufficient to estimate the clinical performance of dental cement. A crown retention test provides more information on the interaction between mechanical and chemical properties. Although the retention forces of crowns cemented with adhesive materials maintained by vacuum effect provided sufficient bond strength, the effect of aging and cyclic loading on the vacuum effect has to be further investigated. Clinical tests, or a cyclic loading approach, may demonstrate whether crowns that mainly adhere to the implant by vacuum effect can endure multidirectional chewing forces. In a clinical study6 no debonding of the crowns cemented to zirconia implants using RUN were reported. The present study investigated axial retention forces. In the oral environment, load transmission is far more complex, and further effects such as humidity and thermal stress affect the bonding to zirconia.15,41 The results Rohr et al
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of the present study should therefore be interpreted with caution. Nevertheless, the results provide a better understanding of how the bonding performance of the cement influences the crown retention force. CONCLUSIONS Within the limitations imposed by the current study, the following conclusions were drawn: 1. Retention forces were higher for adhesive and selfadhesive cement than for temporary cements. 2. The application of primer on the crown and implant abutment increased retention forces only for 1 selfadhesive cement (Panavia SA). 3. The shear bond strength of adhesive and selfadhesive cements to zirconia was not generally higher than for temporary cements. 4. The application of primer on the zirconia surface increased the shear bond strength for the selfadhesive cement Panavia SA and the adhesive cements Multilink Implant, Multilink Automix, Vita Adiva F-Cem, and Panavia V5. 5. The diametral tensile strength varied significantly among the cements. REFERENCES 1. Osman R, Swain M. A critical review of dental implant materials with an emphasis on titanium versus zirconia. Materials 2015;8:932-58. 2. Spies BC, Patzelt SB, Vach K, Kohal RJ. Monolithic lithium-disilicate single crowns supported by zirconia oral implants: three-year results of a prospective cohort study. Clin Oral Impl Res 2016;27:1160-8. 3. Gahlert M, Burtscher D, Pfundstein G, Grunert I, Kniha H, Roehling S. Dental zirconia implants up to three years in function: a retrospective clinical study and evaluation of prosthetic restorations and failures. Int J Oral Maxillofac Implants 2013;28:896-904. 4. Jung RE, Grohmann P, Sailer I, Steinhart YN, Féher A, Hämmerle C, et al. Evaluation of a one-piece ceramic implant used for single-tooth replacement and three-unit fixed partial dentures: a prospective cohort clinical trial. Clin Oral Implants Res 2016;27:751-61. 5. Spies BC, Stampf S, Kohal RJ. Evaluation of zirconia-based all-ceramic single crowns and fixed dental prosthesis on zirconia implants: 5-year results of a prospective cohort study. Clin Implant Dent Relat Res 2015;17:1014-28. 6. Spies BC, Kohal RJ, Balmer M, Vach K, Jung RE. Evaluation of zirconia-based posterior single crowns supported by zirconia implants: preliminary results of a prospective multicenter study. Clin Oral Implants Res 29 March 2016. http://dx.doi.org/10.1111/clr.12842. [ePub Ahead of Print]. 7. Coldea A, Swain MV, Thiel N. Hertzian contact response and damage tolerance of dental ceramics. J Mech Behav Biomed Mater 2014;34:124-33. 8. Rohr N, Coldea A, Zitzmann NU, Fischer J. Loading capacity of implant supported hybrid ceramic crowns. Dent Mater 2015;31:e279-88. 9. Groten M, Probster L. The influence of different cementation modes on the fracture resistance of feldspathic ceramic crowns. Int J Prosthodont 1997;10: 169-77. 10. Burke FJ, Fleming GJ, Nathanson D, Marquis PM. Are adhesive technologies needed to support ceramics? An assessment of the current evidence. J Adhes Dent 2002;4:7-22. 11. Kelly JR. Dental ceramics: current thinking and trends. Dent Clin North Am 2004;48:513-30. 12. Stawarczyk B, Beuer F, Ender A, Roos M, Edelhoff D, Wimmer T. Influence of cementation and cement type on the fracture load testing methodology of anterior crowns made of different materials. Dent Mater J 2013;30:888-95. 13. Atsu SS, Kilicarslan MA, Kucukesmen HC, Aka PS. Effect of zirconium-oxide ceramic surface treatments on the bond strength to adhesive resin. J Prosthet Dent 2006;95:430-6. 14. Yoshida K, Tsuo Y, Atsuta M. Bonding of dual-cured resin cement to zirconia ceramic using phosphate acid ester monomer and zirconate coupler. J Biomed Mater Res B Appl Biomater 2006;77:28-33.
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15. de Souza G, Hennig D, Aggarwal A, Tam LE. The use of MDP-based materials for bonding to zirconia. J Prosthet Dent 2014;112:895-902. 16. Tanıs¸ MÇ, Akçaboy C. Effects of different surface treatment methods and MDP monomer on resin cementation of zirconia ceramics an in vitro study. J Lasers Med Sci 2015;6:174-81. 17. Thompson JY, Stoner BR, Piascik JR, Smith R. Adhesion/cementation to zirconia and other non-silicate ceramics: where are we now? Dent Mater 2011;27:71-82. 18. Lüthy H, Loeffel O, Hammerle CH. Effect of thermocycling on bond strength of luting cements to zirconia ceramic. Dent Mater 2006;22:195-200. 19. Ozcan M, Nijhuis H, Valandro LF. Effect of various surface conditioning methods on the adhesion of dual-cure resin cement with MDP functional monomer to zirconia after thermal aging. Dent Mater J 2008;27:99-104. 20. Kern M, Wegner SM. Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 1998;14:64-71. 21. Mahmoodi N, Hooshmand T, Heidari S, Khoshro K. Effect of sandblasting, silica coating, and laser treatment on the microtensile bond strength of a dental zirconia ceramic to resin cements. Lasers Med Sci 2016;31:205-11. 22. Jardel V, Degrange M, Picard B, Derrien G. Correlation of topography to bond strength of etched ceramic. Int J Prosthodont 1999;12:59-64. 23. Blatz MB, Chiche G, Holst S, Sadan A. Influence of surface treatment and simulated aging on bond strengths of luting agents to zirconia. Quintessence Int 2007;38:745-53. 24. Nothdurft FP, Motter PJ, Pospiech PR. Effect of surface treatment on the initial bond strength of different luting cements to zirconium oxide ceramic. Clin Oral Investig 2009;13:229-35. 25. Li R, Zhou H, Wei W, Wang C, Sun YC, Gao P. Effects of mechanical and chemical pretreatments of zirconia or fiber posts on resin cement bonding. PLoS One 2015;10:e0129690. 26. Otani A, Amaral M, May LG, Cesar PF, Valandro LF. A critical evaluation of bond strength tests for the assessment of bonding to Y-TZP. Dent Mater 2015;31:648-56. 27. Blatz MB, Sadan A, Kern M. Resin-ceramic bonding: a review of the literature. J Prosthet Dent 2003;89:268-74. 28. Hu M, Weiger R, Fischer J. Comparison of two test designs for evaluating the shear bond strength of resin composite cements. Dent Mater 2016;32:223-32. 29. Van Noort R, Noroozi S, Howard IC, Cardew G. A critique of bond strength measurements. J Dent 1989;17:61-7. 30. DeHoff PH, Anusavice KJ, Wang Z. Three-dimensional finite element analysis of the shear bond test. Dent Mater 1995;11:126-31. 31. Sudsangiam S, van Noort R. Do dentin bond strength tests serve a useful purpose? J Adhes Dent 1999;1:57-67. 32. Heintze SD. Clinical relevance of tests on bond strength, microleakage and marginal adaptation. Dent Mater 2013;29:59-84. 33. Heintze SD. Crown pull-off test (crown retention test) to evaluate the bonding effectiveness of luting agents. Dent Mater 2010;26:193-206. 34. Kim SM, Yoon JY, Lee MH, Oh NS. The effect of resin cements and primer on retentive force of zirconia copings bonded to zirconia abutments with insufficient retention. J Adv Prosthodont 2013;5:198-203.
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35. Nematollahi F, Beyabanaki E, Alikhasi M. Cement selection for cementretained implant-supported prostheses: a literature review. J Prosthodont 2016;25:599-606. 36. Sellers K, Powers JM, Kiat-Amnuay S. Retentive strength of implantsupported CAD-CAM lithium disilicate crowns on zirconia custom abutments using 6 different cements. J Prosthet Dent 2017;117:247-52. 37. Holderegger C, Sailer I, Schuhmacher C, Schläpfer R, Hämmerle C, Fischer J. Shear bond strength of resin cements to human dentin. Dent Mater 2008;24: 944-50. 38. Stawarczyk B, Hartmann R, Hartmann L, Roos M, Özcan M, Sailer I, et al. The effect of dentin desensitizer on shear bond strength of conventional and self-adhesive resin luting cements after aging. Oper Dent 2011;36:492-501. 39. Bähr N, Keul C, Edelhoff D, Eichberger M, Roos M, Gernet W, et al. Effect of different adhesives combined with two resin composite cements on shear bond strength to polymeric CAD/CAM materials. Dent Mater J 2013;32: 492-501. 40. Blumer L, Schmidli F, Weiger R, Fischer J. A systematic approach to standardize artificial aging of resin composite cements. Dent Mater 2015;31: 855-63. 41. Wolfart M, Lehmann F, Wolfart S, Kern M. Durability of the resin bond strength to zirconia ceramic after using different surface conditioning methods. Dent Mater 2007;23:45-50. 42. Yoshihara K, Nagaoka N, Sonoda A, Maruo Y, Makita Y, Okihara T, et al. Effectiveness and stability of silane coupling agent incorporated in “universal” adhesives. Dent Mater 2016;32:1218-25. 43. Matinlinna JP, Vallittu PK. Bonding of resin composites to etchable ceramic surfaces-an insight review of the chemical aspects on surface conditioning. J Oral Rehabil 2007;34:622-30. Corresponding author: Dr Nadja Rohr Division of Dental Materials and Engineering Department of Reconstructive Dentistry and Temporomandibular Disorders University Center for Dental Medicine University of Basel Hebelstrasse 3 CH-4056 Basel SWITZERLAND Email: [email protected] Acknowledgments The authors thank Vita Zahnfabrik, Bad Säckingen, Germany, for supporting this study with materials. Copyright © 2017 The Authors. Published by Elsevier Inc. on behalf of the Editorial Council for The Journal of Prosthetic Dentistry. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).
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